The present invention relates to an fine actuator wherein a light beam is used for reading data from a recording medium and writing data onto it.
An example of a conventional fine actuator will be explained as follows, referring to drawings. FIG. 9 is a front view of a conventional fine actuator and FIG. 10 is a top view of the fine actuator shown in FIG. 10.
In the figures, the numeral 1 represents a base, and 2 represents a lens-holder that holds objective lens 3.
On both sides of the lens-holder 2, there are provided respectively first coil 4 and second coil 5 each consisting of a tracking coil and a focusing coil.
The numerals 6 and 7 represent the first magnetic circuit and the second magnetic circuit both provided on the base 1. In the magnetic gaps of these magnetic circuits, there are provided respectively the first coil 4 and the second coil 5 mentioned above.
The numerals 8 and 9 represent respectively the first supporting pole and the second supporting pole each provided on the back of each yoke of the first and second magnetic circuits 6 and 7 on the base 1.
The numerals 10 and 11 represent the first tracking leaf spring and the second tracking leaf spring each of which is fixed, at one end, on each of supporting poles 8 and 9 and is flexible in the direction of tracking.
The numeral 12 is a relay member to which the other end of each of the first and second tracking leaf springs is fixed.
The numerals 13 and 14 represent respectively the first focusing leaf spring and the second focusing leaf spring both being flexible in the focusing direction, and one end of each is fixed on the relay member 12 and the other end of each is fixed on the lens-holder 2.
Next, operations in the aforesaid arrangement will be explained. When focusing, an electric current is applied to coils of the first coil 4 and the second coil 5 from an unillustrated control circuit. Thereby, a thrust is generated in each of the first coil 4 and the second coil 5, causing the lens holder 2 to move in the direction of arrow F in FIG. 9 against the resilience of focusing leaf springs 13 and 14. When the supply of electric current is cut, the lens holder 2 returns to its original position.
Next, when conducting tracking, an electric current is applied to each tracking coil in the first coil 4 and the second coil 5 from an unillustrated control circuit. Thereby, a thrust is generated in each of the first coil 4 and the second coil 5, causing the lens holder 2 to move in the direction of arrow T in FIG. 10 against the resilience of focusing leaf springs 10 and 11. When the supply of electric current is cut, the lens holder 2 returns to its original position.
In an fine actuator having a constitution like those mentioned above, an optical axis for objective lens 3 is inclined very little and less friction is caused in operation, resulting in excellent characteristics of tracking and focusing.
Next, the second example of a conventional fine actuator will be explained, referring to FIGS. 19 and 20. In these drawings, parts or components which are the same as those in FIGS. 9 and 10 are given the same symbols and explanations for them will be omitted. Differences between the present example and the first example for a conventional fine actuator include the first focusing leaf spring 15 and the second focusing leaf spring 16. Each of these focusing leaf springs 15 and 16 has on its both edges respectively the through holes 15a and 15b, and 16a and 16b.
These provided holes 15a and 15b, and 16a and 16b contribute to lower the stiffness at both edges of the leaf spring and thereby to virtually eliminate resonance of a high order.
Recently, however, the trend for a small recording medium compels an optical disk apparatus employing a fine actuator like those mentioned above to be also small.
However, in the example of a conventional fine actuator having the constitution mentioned above, when a length of each of focusing leaf springs 13 and 14 is shortened for the purpose of smaller size, a length of each of tracking leaf springs 10 and 11, which are to be shorter than the focusing leaf spring is further shortened.
When the length of a spring is shortened, the stiffness of the spring is increased, which causes a fine actuator to be unable to secure a sufficient distance for its movement.
In order to overcome the problem mentioned above, the thickness of a spring can be reduced. However, existing thickness of a spring is as thin as several tens .mu.m, which is very thin, and any thinner than this may adversely affect assembling work.
The invention has been devised in view of the aforesaid problem and its object is to provide a small-sized fine actuator.
Further, a fine actuator of this type is generally mounted on the top of an optical unit and is provided with a reading unit wherein a yoke having a magnetic driving circuit is provided with an objective lens unit having therein an induction coil that follows the aforesaid driving circuit through a supporting member that supports horizontally the objective lens unit so that it can move freely in the focusing direction. Thus track signals on the surface of an optical disk are subjected to reading/writing through the objective lens unit.
For example an induction coil which can follow direction X (track servo direction) and direction Z (focus servo direction) is provided on the side of the objective lens unit. Thus, a fine actuator that can follow a magnetic induction circuit on the yoke side is formed, and track signals on the surface of the optical disk can be sent to or received by the optical unit through an opening provided on the yoke. In this case, it is necessary to adjust finely inclination of the objective lens unit against the optical disk surface so that the objective lens unit can be focused without aberration on the optical disk surface.
For the requirement mentioned above, a conventional device has employed either one of the following systems.
(1) Spacer system
(2) Screw-tightening system
In the spacer system, in this case, spacer S (a flake) whose thickness is precisely controlled has been placed at each of three points between optical unit 111 and yoke 121 as shown in FIG. 23. In this way, inclination of yoke 121 against optical unit 111 has been adjusted by means of an optimum combination of spacers S each having a different thickness, thus, the inclination of objective lens unit 141 supported by supporting member 131 has been adjusted.
The screw-tightening system, on the other hand, has been constructed so that a protrusion of yoke 122 is inserted in recess 112 that is provided on the top of optical unit 111 and the protrusion is tightened together with the recess 112 by screws N at three points for adjustment, as shown in FIG. 24. Thus, the inclination of yoke 122 against optical unit 112 has been adjusted by controlling the tightening force for each screw N, and the inclination of objective lens unit 142 supported by supporting member 132 has been adjusted.
In the mechanism for adjusting inclination of the objective lens unit in a conventional optical disk device, the spacer system (1) has not been free from a disadvantage that it is troublesome to handle because the spacer is very thin and very small. Further, workability thereof has been very poor because of the necessity for adjusting by means of an optimum combination of spacers each having a different thickness.
On the other hand, the screw-tightening system has a disadvantage that intensive stress is generated on each of a yoke and an optical unit, though it only requires adjustment for tightening of three screws and it is free from troublesome handling as in the spacer system. In particular, optical parts in an optical unit, even when they have minute strains as small as the size of a wavelength, are feared to affect a signal-detection function adversely, which is undesirable.
In view of the aforesaid point, the second object of the invention is to provide an optical disk device provided with an inclination adjustment mechanism which only requires simple adjustment and which does not cause stress on an optical unit.